The present invention relates to a hydraulic damper, such as a suspension strut or shock absorber, for the suspension system of a motor vehicle. In particular, the present invention relates to a hydraulic damper of the single or monotube type.
Known hydraulic dampers of the monotube type comprise a tube; a rod guide positioned at one end of the tube; a floating piston positioned inside the tube; a compensation chamber formed between the floating piston and the other end of the tube; a piston assembly sealably slidably mounted in the tube between the floating piston and the one end of the tube, the piston assembly separating a compression chamber from a rebound chamber within the tube; and a piston rod connected to the piston assembly and extending through the rebound chamber and the rod guide. The rebound chamber and the compression chamber are normally filled with hydraulic fluid. The compensation chamber is normally filled with gas. The piston assembly includes a rebound stroke valve and a compression stroke valve for controlling flow of fluid between the rebound chamber and the compression chamber.
In these known arrangements, if the hydraulic damper is subjected to a high speed compression stroke (such as when an associated wheel of a motor vehicle passes over a pot hole in the road) there is a risk that the compression stroke valve will not open quickly enough to allow adequate fluid flow from the compression chamber to the rebound chamber. In such cases, the damper does not work properly and the vehicle body may be damaged. Also, in such cases, a vacuum may be generated in the rebound chamber which can result in the seal between the piston rod and the rod guide opening to allow air into the rebound chamber. With this seal being open, the subsequent high speed rebound stroke may force fluid out of the rebound chamber pass the seal.